Method and apparatus for roasting ore



Aug; 17, 1937. R. B. FERGUSON METHOD AND APPARATUS FOR ROASTING ORE Filed July 24, 1935 INYENTOR Robe/f B. Ferguson Patented Aug. 17, 1937 UNITED STATES METHOD AND APPAgIATUS FOR ROASTING Robert B. Ferguson, Plainfield, N. J., assignor to General Chemical Company, New York, N. Y., a'corporation of New York Application July 24, 1935, Serial No. 32,849

8 Claims.

This invention is directed to methods and apparatus for roasting metal sulfides, and more particularly for roasting finely divided sulfides to desulfurize the same and to produce sulfur dioxide for use in the manufacture of sulfuric acid, or for any other purposes desired.

The nature of the invention, and the objects and advantages thereof may be more fully understood from a consideration of the following description taken in connection with the accompanying drawing, in which- Figure 1 is a vertical section of a preferred burner construction;

Fig. 2 is an enlarged vertical section similar to portions of Fig. l and taken through the ore feeding mechanism, and

Fig. 3 is an enlarged vertical section taken through an air inlet port.

Referring to the drawing, l0 designates a shaft burner comprising a steel shell or casing H within which is placed the furnace lining I2, constructed of suitable refractory material such as firebrick and defining a roasting chamber it of circular horizontal cross-section. The upper part of the combustion chamber is closed off by a crown l5 the top side of which forms a drying or preheating hearth ii. The shell I! projects upwardly beyond the crown l5 and carries a steel framework l8 which supports rabbling mech- 3 anism for the drying hearth. The surface of hearth I1 is slightly cone-shaped and slopes downwardly toward the shell of the furnace. Lying above the hearth are rabble arms l9 having downwardly projecting plows 20 pitched to work sulfides gradually toward the circumference of the drying hearth. Arms l9 are rotated by a motor 22 through a shaft 23 supported in bearings so as to maintain the lower ends of the plows 2d spaced with respect to the surface of the drying hearth 40 ll. Fines are intermittently dropped from distributing platform 25 onto the center of hearth I! by a sweep 21 rotating with shaft 23.

As shown more clearly in the enlarged detail of Fig. 2, attached to shell I l by suitable brackets 45 not shown are hoppers covered by sloping screens 3|. Cut through the shell ll and also in the upper edge of lining I! are downwardly sloping passages or conduits 34 through which fines are passed from drying hearth ll into hoppers 35B. 50 Oversized material ,discharged by screens 3| is colected by receptacles 32 and conveyed by means not shown to a crusher, or used in a bed roaster or otherwise disposed of. It will be understood the number of conduits 34 and hoppers 30 used 55 in conjunction with the burner correspond with (or. 75-9) v i the number of injectors employed. On rotation of rabble arms 19 the sulfide fines are gradually fed through opening 34 intohopper 30 which discharges fines into a downwardly sloping passage 36 which together with air inlet 31 constitutes part of an ore injector. For convenience in construction, fines passage 36 and air inlet 31: may be made in an individual block, several of which, in accordance with the number of injectors used, are peripherally spaced about the upper end of the burner. As will be seen from Fig. 2, sulfides fed into passage 36 from hopper 3t run down over sloping surface 40 at the bottom of which the fines are picked up by the air stream flowing through passage 31 and are carried into the furnace in a horizontal direction through fines inlet port 62. In some cases the axis of air inlet passage 3'! may be upwardly directed at a relatively low angle with the horizontal. r In the embodiment of the burner illustrated in Fig. '1 six injectors are employed.

The air used in the process to inject fines into the furnace and also to provide oxygenfor the roasting operation is introduced into the roaster through pipe 65 opening into the bottom of an air preheating jacket Ml preferably made so as to surround the vertical walls of the burner. Near the top, the roaster is surrounded by a casing 50 formed so as to provide a secondary air inlet bustle 52 and a primary air inlet bustle 56 which communicates directly with the upper end of heating jacket ll. The casing 50 is attached to the shell in such a way that the outer ends of the air inlets 3'? open into primary air bustle 58. Flow of air from bustle 5i into air inlet Si is controlled by a suitable valve 56 operable by valve stem 5'8 from outside casing Ell.

The major portion of the air used for oxidation of the fines is introduced into the top of combustion chamber M through ports 60 communicating through passages 62, Fig. 3, with secondary air inlet bustle 52. As will be seen from Figs. 2 and 3, the inner edge of the top side 64 of casing 50 abuts burner shell II, with the exception of the modified portions formed to accommodate the lower ends of hoppers 30 as shown in Fig. 2. Flow of air from primary air bustle 51 into secondary air bustle 52 through a plurality of passages 66 is controlled by a corresponding number of suitable independently or simultaneously operated valves 61. Where it is desired to operate with unpreheated air, pipe maybe connected directly with bustle 54 and jacket 41 eliminated. Alternatively, some of the air. may be introducedrthrough pipe 45 as shown on the drawing and the balance through a pipe 55 connected to inlet bustle I4 as shown in Fig. 2. In either case, the air may be supplied by a blower not shown. g In accordance with the invention, scarring or the building up of slag-like accretions onthe inner walls of the roasting chamber is prevented by introducing at least some of the air consumed in roasting in such a way as to provide in effeet a .blanket or layer of air interposed be- I tween at least a portion of the inner walls of the roasting chamber and burning ore. To facilitate maintenance of the air blanket, there is provided in the burner walls a plurality of ports 10 ,communicating with the primary air inlet bustle 54 by means of passages II. Ports 10 are spaced about the periphery of the roasting chamber at intervals suitable for the particular operating requirements. As shown in Pig. 2, ports III open into combustion chamber ll underneath deflecting plate 12 having a depending vertical "portion I; long enough to insure downward passage of air along the inner wall of the combustion chamber for a substantial distance. Flow of air through all passages Il may be controlled by valves I5 provided with operating stems 16.

The bottom of the combustion chamber I4 is formed by a hopper-shaped brick hearth l8 terminating in a cinder outlet pipe 19 emptying into a pit 00 from which cinder may be discharged by a conveyor not shown. A gas main 8| for withdrawing gaseous prodnets of combustion from the burner connects the bottom of the burner with the lower end of a preliminary gas cooler 82. As shown on the drawing, the cooler is constructed generally similar to-burner II and comprises chiefly a steel shell 84 and a lining I! of refractory material forming an elongated cylindrical gas cooling 40 chamber 86. The upper surface 81 of top 88 of the cooling chamber 86 forms 'a drying or preheating hearth which is slightly cone-shaped and slopes downwardly toward shell 84. Above the,

hearth I! are rabble arms 90 carrying downwardly projecting plows 9| pitched to work sulfides gradually toward the circumference of the v drying hearth. Arms 90 are rotated by a motor 93 through shaft 04 supported in bearings so as to maintain the lower ends of the plows spaced with respect to the surface of hearth 81. A bin ll mounted on framework 96 discharges fines onto a platform 01 from which the fines are intermittently dropped onto hearth 81 by a sweep ll, rotating with shaft 94. The upper edge of cooler shell 84 and also-the upper edge of lining OI are provided with a passage I 00 through which material is fed into chute III, the outlet end of which is arranged to discharge fines onto platform II on the top of'burner ll.

00 The lower end of chamber 86 is made hoppershaped and terminates in an outlet pipe in connecting with an air-lock ill by means of which dust and cinder may be discharged from chamber 06 without admitting air into the system.

Sulfur dioxide gases leave. the top of gas cooling chamber ll through a pipe III.

The invention is applicable to roasting of finely divided metal sulfides such as iron pyrites, pyrrhotite, zinc sulfide or arsenopyrite, and for convenience the operation of the process may be -describedinconnectionwithroastingofiron The supply of sulfide fines is maintained in bin II by a suitable conveyor or elevator mechanism is not shown. Before the'rossting operation is begun, the combustion chamber I4 is preheated to temperatures above the ignition point of the particular fines to be roasted as by means of oil burners inserted through conveniently located work-holes not shown. After an initial supply of fines has been provided on burner hearth l1 and the desired degree of preheat, obtained in combustion chamber ll, motors 22 and OJ are started and rabble arms is and I. may be rotated at a rate of say one revolution per minute. The fines run continuously out of bin OI onto platform 91 and on each revolution of shaft 04 a reg ulated quantity of fines is swept oi! platform 01 onto approximately the center of the gas cooler drying hearth 81. On rotation of rabble arms 90, sulfide fines are gradually worked across the surface of hearth l1 and into outlet passage Ill opening into chute IOI which carries the more or less dried fines on the platform 25 from whence such fines are intermittently dropped onto the I center of drying hearth ll on top of the burner.

By rotation of the rabble arms ii, the fines are worked outwardly across the surface of hearth l1 and into theseveral pes 34 each of which communicates'with a hopper 3!. The dry or dry and partly preheated fines are-run onto sloping screen II, which removes lumps and thence into hopper 30 and injector feedpassages ll.

. In accordance with the invention, only a relatively small amount,'say less than about 10%,

of the total air Win the roasting operation is employed to inject the fines into the top of the roasting chamber. Steam or any gas not adversely affecting oxidation of the sulfite may be employed to charge the flnes'into the combustion chamber. However, it is preferred to use air which may be maintained in bustle I at a pressure of for example about 5 pounds per square inch. Since the'air is brought'into the process throush jacket 41, the air in bustles. I2 and I may be preheated iosay 300-400' F. by absorption of heat from the burner walls. l'ines run continuously down through c It and arepicked up by the air stream passing through injector inlet passage 31. The quantity and velocity of air fiowing through any given passage 81 is controlled by adjustment of a valve II, and in practice, the valve is adjusted so that the primary air flows through passage 81 in quantity and at velocity great enough so that the bulk of the fines particles are carried substantially horizontally over a substantial distance through the upper end of the combustion chamber before descending under the infiue'nee of gravity. In Fig. 1 dotted line I" indicates the approximate path of an ore particle of average sise. Further,

theairpressureinpasssgeilisregulatedpreferably so that substantially none of'the fines particleswillbecan'iedfsr enough across thefurnace horisontally so as to contact the opposite important. since the finesoontaining an appleciable proportionof sulfur are in a state condueive to scar formation. Horizontal orslightly upwardlyinclinedinjectionoffinesalsohsstbe advantage of eifecting heating up of the fines to the ignition point before of the fines,inthiswsydecressingthenee- 60 wall of the combustion chamber. Inasmuch as essary length of the vertical drop for desulfurization of the fines and cutting down the vertical dimension of the burner.

In accordance with the invention the major part of the air used to support roasting is introduced through the air ports 60 communicating with the secondary air inlet bustle 52. By adjustment of the several valves 61, the air pressure in secondary air bustle 52 and the velocity and quantity of air entering the combustion chamber through ports 60 may be regulated. To obtain the best results, it is preferable to maintain the pressure in bustle 52 at say around 3 pounds per square inch, appreciably less than the pressure in bustle 54 so that the velocity of the air entering the combustion chamber through ports 60 is substantially less than the velocity of the air fiowing through injector inlets 31. The horizontal plane of ports 60 is located adjadent the underside of combustion chamber crown l5 substantially above the horizontal plane of ports 42 through which the fines are injected. By reason of this arrangement and the relatively low velocity of the air entering the combustion chamber through ports 60, the relatively large amount of air needed for roasting can be introduced into the upper end of the combustion chamber just beneath the crown l5 without immediately contacting and disturbing the fines dispersion formed approximately in the plane of inlets 31. In this way, the setting up within the upper end of the roaster of turbulent conditions tending to carry the fines against the roasting chamber walls while in a state conducive to scarring is avoided. Separate introduction of the fines and of the bulk of the air used in the roasting operation makes possible the introduction into the top of a relatively short furnace of all the fines and of all the air needed to support roasting without causing fines to contact with the inner walls chamber.

- of the roasting chamber as a whole may be around 1800-2000 F.

In the upper end of the roasting chamber, the reaction is most intense and temperatures are high on account of the relatively high sulfur content of the ore. Accordingly, in the upper end of the combustion zone there is a greater tendency toward scar formation than farther down. By introducing the fines and the major portion of the air used to support oxidation into the upper end of the roasting chamber in the manner described, the tendency toward causing contact of fines with the roasting chamber wall is minimized, but to insure substantial absence of scarring in the roasting operation in accordance with the present invention a relatively small portion of the primary air is introduced into the top of the combustion chamber through ports beneath deflecting plate 12. The pressure of the air flowing through passages H is adjusted by valves so that there is maintained between of the combustion the roasting chamber walls and the burning fines an air blanket extending down at least a substantial distance toward the'bottom of the combustion chamber. As roasting of the fines progresses, scar formation tendency decreases and usually it is not necessary to maintain an air blanket between the roaster chamber walls and the burning fines all the way to the bottom of the combustion zone. In practice, the lower edge of the zone in which scar formation tends to take place may be determined by observation through work-holes, and the air pressure in passages H adjusted accordingly so as to cause the air blanket to extend downwardly at least throughout the zone in which scar formation tends to takew place. Only a relatively small amount, say about 5%, of the total quantity of air required for roasting need be used to maintain the air blanket.

The fines and the oxidizing gas stream pass downwardly co-current through the combustion chamber and roasting of the fines progresses to completion. It is preferred to use an unobstructed combustion chamber of relatively large crosssection and having a horizontal dimension ap-' proximating and preferably a little less than the height. The co-current roasting operation may be carried out satisfactorily when fines and air are introduced into the burner in the manner described and the combustion chamber is prcportioned about as indicated.

A free-flowing iron oxide cinder collects on hearth l8 and is discharged from the apparatus into pit 80. The hot sulfur dioxide gases at temperatures around 1800-2000 F. pass through connection 8| and thence upwardly through chamber 86. gas stream while the latter flows upward through chamber 85 and collects in the bottom. The horizontal dimension of cooler 82 corresponds generally with that of burner 10, although the height of the cooler is preferably sufficient to make possible gravity fiow of fines'through chute llll. In view of the large area presented to the atmosphere by the surface of the cooler, substantial cooling of the gas is effected, and the sulfur dioxide gas stream is discharged through pipe I05 at temperatures of about 1200-1400" F.

Entrained dust drops out of the and is conducted thence to a gas purification the fines may be satisfactorily injected into and dispersed in the combustion chamber. The amount of drying surface of a single burner unit is relatively limited, and the capacity of a single burner unit depends more or less upon the amount of relatively dry fines available. By the present arrangement, the area of the fines drying surface is substantially doubled, and by utilizing heat of the hot sulfur dioxide gases recovered during cooling of the gases after discharge from the burner, the capacity of a burner unit may be substantially increased without providing additicnal fines drying equipment.

I claim:

1. The method for roasting metal sulfide fines to produce sulfur dioxide which comprises intion point of the fines and having a large transverse dimension relative to'the height, said fines being injected into the combustion'chamber in a direction having an initial horizontal component and at an initial velocity such as to cause at least a portion of the fines to travel horizon.- tally across the combustion chamber a substantial distance and to di perse the fines in the combustion zone and low enough to prevent initial contact of any substantial quantities of incoming fines with the heated combustion chamber walls at points approximately opposite the point of introduction of the fines, separately introducing into said end of the combustion chamber at a point adjacent introduction of the fines a stream of oxidizing gas containing sufiicient oxygen to efiect substantially complete roasting of the fines and moving at 'a velocity less than that of the initial injection velocity of the fines and low enough to avoid setting up turbulent gas currents in the combustion chamber and to avoid causing fines contacting the hot walls of the combustion chamber, roasting the fines while in suspension in the oxidizing gasandvwhile passing the fines through the combustion chamber cocurrent with the stream of oxidizing gas, separating gaseous combustion products from oxide cinder, discharging cinder from the bottom of the combustion chamber, and separately withdrawing gaseous combustion products therefrom.

2. The method for roasting metal sulfide'fines to produce sulfur dioxide which comprises injecting sulfide fines into one end of a combustion chamber heated to temperatures above .the ignition point of the fines and having a large. transverse dimension relative to the height, said fines being injected into the combustion chamber in 40 a direction having an initial horizontal component by means of a stream of gas at superatmospheric pressure and having velocity such astocauseatleastaportionoi'thefinesto travel horizontally across the combustion chamher a substantial distance and to disperse the fines in the combustion zone and low enough to prevent initial contact of any substantial quantitles of incoming fines with the heated combustion chamber walls at points approximately opposite the point of introduction of the fines,

separately introducing into said end of the com,- bustion chamber at a point adjacent introduction of the fines a stream of oxidizing gas containing suillcient oxygen to effect substantially complete roasting of the fines and moving at a velocity less than that of'the fines injecting gas and low enough to avoid setting upturbulent gas currents in the combustion chamber and to avoid causing fines contacting the hot walls of the combustion chamber, roasting the fines while in suspension in the oxidizing gas and while pass ing the fines through the combustion chamber co-current with the stream of oxidizin 8". 8 P- arating gaseous combustion products from oxide cinder, discharging cinder from the bottom of the combustion chamber, and separately withdrawing gaseous combustion products therefrom.

- 3. The method for roasting metal sulfide fines to produce sulfur dioxide which comprises injecting sulfide fines into the top of a combustion chamber heated to; temperatures above the ignition point of the fines and having a large transverse dimension relative to the height, said fines being injected into the combustion chamber in a direction having an initial horizontal component by means of a stream of gas at superatmospheric pressure and having velocity such as to cause at least a portion of the fines' to travel horizontally across the combustion chambers substantial distance and to form a dispersion of fines in the upper end ofthe combustion chamber and low enoughto prevent initial contact of any substantial quantities of incoming fines with the heated combustion chamber wallscombustion chamber and to avoid causing fines contacting the hot walls of the combustion chamber, roasting the fines while in suspension in the oxidizing gas and while passing the fines down-' wardly through the combustion chamber co-current with the stream of oxidizing gas, separating gaseous combustion products from oxide cinder, discharging cinder from the bottom of the combustion chamber, and separately withdrawing gaseous combustion products from the bottom of the combustion chamber.

4. The method for roasting metal sulfide fines to produce sulfur dioxide which comprises injecting sulfide fines peripherally into one end of a combustion chamber heated to temperatures above the ignition point of the fines and having a large transverse dimension relative to the height, said fines being injected into the combustion chamber by means of a stream of gas at superatmospheric pressure and having velocity such as to cause. atleast a portion of the fines -to travel horizontally across the combustion chamber a substantial distance and to disperse the fines in the combustion zone and low enough to prevent initial contact of any substantial quantities of incoming fines with the heated combustion chamber walls at points approximately opposite the point of introduction of the fines,

separately introducing peripherally intosaid end I of the combustion'chamber, at a point adjacent but spaced from the point of introduction of the fines, a stream of oxidizing gas containing sufilcient oxygen to effect substantially complete roasting of the fines and moving at a velocity substantially less than that of the fines injecting gas and low enough'to avoid setting up turbulent gas currents in the combustion chamber and to avoid causing fines contacting the hot walls of the combustion chamber, roasting the fines while in suspension in the oxidizing :gas, separating gaseous combustion products from oxide cinder, discharging cinder from the bottom of the combustion chamber, and separately withdrawing gaseous combustion products therefrom.

5. The method for roasting metal sulfide fines to produce sulfur dioxide which comprises injecting sulfide fines peripherally at the top of a com.

bustion chamber heated to temperatures above the ignition point of the fines and having a large transverse dimension relative to the height. said fines being injected into the combustion chamber by means of a stream of air at superatmospheric pressure and having velocity such as to cause at least a portion of the fines-to travel horizontally across the combustion chamber a substantial distance and to form a dispersion of fines in the upper end of the combustion chamberficient oxygen to ber at the top and low enough to prevent initial contact of any substantial quantities of incoming fines with the heated combustion chamber walls at points approximately opposite the point of introduction of the fines, separately introducing peripherally and at the top of the combustion chamber, at a point adjacent but spaced from the point of introduction of the fines, a stream of air containing sufefiect substantially complete roasting of the fines and moving at a velocity substantially less than that of the fines injecting air and. low enough to avoid setting up turbulent gas currents in the combustion chamber and to avoid causing fines contacting the hot walls of the combustion chamber, roasting the fines while in suspension in the oxidizing gas and while passing the fines downwardly through the combustion chamber co-current with the stream of oxidizing gas peripherally introducing into the top of the combustion chambera stream of air and maintaining a layer of said air between the walls of the combustion chamber and the burning ore while the latter is in a state conducive to scar formation, separating gaseous combustion products from oxide cinder, discharging cinder from the bottom of the combustion chamber, and separately withdrawing gaseous combustion products from the bottom of the combustion chamber.

6. Apparatus for roasting metal sulfide fines comprising a combustion chamber having a large horizontal dimension relative to the height, a fines feeding conduit in the periphery of the combustion chamber at the top thereof, means for feeding fines into the inlet end of the feed conduit, means for injecting gas into the fines to charge the same into and cause fines to travel across the combustion chamber a substantial distance in a horizontal direction and form a dispersion of fines in the top of the combustion chamber, a plurality of air ports in the periphery of the combustion chamthereof for introducing into the top of the combustion chamber a stream of oxidizing gas to support oxidation of the fines, means for discharging cinder from the bottom of the combustion chamber, and a gas outlet for withdrawing gaseous combustion products from bottom of the combustion chamber.

'1. Apparatus for roasting metal sulfide fines comprising a combustion chamber having a large horizontal dimension relative to the height, a plurality of fines feeding conduits in the periphery of the combustion chamber at the top thereof, means for feeding fines into the inlet ends of the feed conduits, means for injecting gas into the fines to charge the same the combustion chamber into the combustion chamber and cause fines to travel across the combustion chamber a substantial distance in a horizontal direction and form a dispersion of fines in the top of the combustion chamber, a plurality of air ports in the periphery of the combustion chamber at the top thereof for introducing into the top of the combustion chamber a stream of oxidizing gas to support oxidation of the fines, means at the upper end of the combustion chamber for maintaining a layer of gas between at least the upper part of the combustion chamber walls and the burning ore therein, means for discharging cinder from the bottom of the combustion chamber, and a gas outlet for withdrawing gaseous combustion products from the bottom of the combustion chamber.

8. The method for roasting metal sulfide fines to produce sulfur dioxide which comprises injecting sulfide fines peripherally at the top of a come bustion chamber heated to temperatures above the ignition point of the fines and having a large transverse dimension relative to the height, said fines being injected into the combustion chamber by means of a stream of air at superatmospheric pressure and having velocity such as to cause at least a portion of the fines to travel horizontally across the combustion chamber a substantial distance and to form a dispersion of fines in the upper end of the combustion chamber and low enough to prevent initial contact of any substantial quantities of incoming fines with the heated combustion chamber walls at points approximately opposite the point of introduction of the fines, separately introducing peripherally and at the top of the combustion chamber, at a point adjacent but spaced v from the point of introduction of the fines, a stream of air containing suificient oxygen to effect substantially complete roasting of the fines and moving at a velocity substantially less than that of the fines injecting air and low enough to avoid setting up turbulent gas currents in the combustion chamber and to avoid causing fines contacting the hot walls of the combustion chamber, roasting the fines while in suspension in the oxidizing gas and while passing the fines downwardly through the combustion chamber cocurrent with the stream of oxidizing gas, separating gaseous combustion products from oxide cinder, discharging cinder fromthe bottom of the combustion chamber, and "separately withdrawing gaseous combustion products from the bottom of the combustion chamber.

ROBERT E. FERGUSON. 

